1. Field of the Invention
This invention relates to a method of reducing the purine content of an edible material. The method comprises treating an edible material having a first level of purine content with a microorganism capable of digesting purine compounds, such that the thus treated edible material has a second level of purine content lower than the first level of purine content. The microorganism is selected from the group consisting of Aspergillus oryzae ATCC 11493 (BCRC 30118), Aspergillus oryzae ATCC 26850 (BCRC 30133), Aspergillus oryzae ATCC 44193 (BCRC 30222), Aspergillus oryzae ATCC 26831 (BCRC 30235), Rhizopus oryzae ATCC 52362 (BCRC 31108), and combinations thereof. This invention also relates to an edible material obtained from the aforementioned method.
2. Description of the Related Art
Gout is a disease resulting from deposition of monosodium urate crystals, which is induced by overproduction or underexcretion of uric acid. Generally, more than 90% of uric acid exists in a form of monosodium urate at pH 7. Monosodium urate crystals may deposit in articular cartilage, synovial fluid, tendon, and other soft tissues, or may form uric acid stones in kidney. Gout normally correlates to increase of serum uric acid levels, and clinical symptoms thereof include acute and chronic arthritis, tophi, interstitial renal disease, uric acid nephrolithiasis, etc.
A male with a serum uric acid level higher than 7 mg/dL (420 μmol/L) and a female with a serum uric acid level higher than 6 mg/dL (360 μmol/L) are regarded as having hyperuricemia. Hyperuricemia is a factor in development of gout. However, relationship between hyperuricemia and acute gout is still uncertain. Furthermore, hyperuricemia is found to be associated with development of hypertriglyceridemia, diabetes mellitus, and coronary artery disease.
Uric acid is the final metabolism product of purine and is excreted in urine. Many pathological studies indicate that ingestion of purine-rich food is the cause of gout and hyperuricemia. Due to over-ingestion of the purine-rich food, obesity, etc., incidence and prevalence regarding gout and hyperuricemia have gradually increased. Moreover, patients with gout or hyperuricemia tend to be younger. Therefore, reduction of purine ingestion is considered as an effective way to prevent gout and hyperuricemia.
Examples of the purine-rich food are mushrooms, legumes, meat, seafood, soft roe, eggs, alcoholic beverages, and so forth. Most of the purine-rich food contains abundant nutrition and many biologically active ingredients. Since the purine-rich food may give rise to gout, the same is not suitable for everyone. Consequently, effectively reducing the purine content of the purine-rich food is an important goal.
Examples of conventional physical and chemical methods for reducing the purine content of the purine-rich food include processing treatment (e.g., washing, boiling, steam cooking, roasting, and drying) for lowering the purine content of seafood (e.g., fish and shrimp), use of adsorbent (e.g., activated charcoal and zeolite) for removing purine compounds in fermented malt beverages, and reduction in amount of barley malt and dilution treatment for reducing the purine content of beers.
In recent years, biological methods (such as biodecomposition) of reducing the purine content of food are highly regarded.
G. D. Vogels and C. Van Der Drift have reported that Aspergillus oryzae is able to generate xanthine dehydrogenase (XDH), uricase (Uri), allantoinase (An), and allantoicase (Ac) (G. D. Vogels and C. Van Der Drift (1976), Bacteriol. Rev., 40:403-468). Aspergillus oryzae is usually used to produce soybean sauce, miso, vinegar, sweet bean sauce, and so forth, and is also applied to generate various enzymes such as amylase and protease.
Rhizopus oryzae is a filamentous fungus, and is frequently used to produce alcoholic beverages and various organic acids such as fumaric acid, succinic acid, oxalic acid, citric acid, and lactic acid.
U.S. Pat. No. 6,013,288 discloses a process for manufacturing beer having a reduced content of purine compounds by using wort having a reduced content of purine nucleosides as a result of decomposing purine nucleosides into purine bases by using isolated purine nucleoside phosphorylase and/or isolate purine nucleosidase. The purine nucleosidase may be obtained from the genera Aspergillus (e.g., Aspergillus oryzae (IAM 2630)), Bacillus, Saccharomyces, etc.
There is still a need in the art to provide a method of efficiently reducing the purine content of food.